The field of this invention generally relates to construction, and more particularly to an apparatus for positioning and retaining a bolt while concrete or the like is poured around it.
Most buildings require a foundation. In many instances, this foundation is a concrete slab, created on the building site by pouring concrete into a wooden form, commonly referred to as a mud wall. In general, the mud wall is made of lumber, most commonly a 2.times.8 or stacked 2.times.8s.
It is generally advantageous to secure a building to its concrete slab foundation. By securing the structure to the slab, the structure is less likely to move off the foundation during a hurricane, tornado, earthquake, mudslide or other natural disaster. One way to secure a structure to a foundation is by using anchor bolts, so named because one end of an anchor bolt is anchored in the concrete foundation. This is typically accomplished by submerging one end of the anchor bolt in the wet concrete of the foundation as it is being poured and holding the anchor bolt in position until the concrete dries. The end of the anchor bolt protruding out of the foundation is typically threaded to receive a nut or other correspondingly-threaded object. The structure is typically anchored to the foundation by placing onto the anchor bolts a sill plate containing holes corresponding to the locations of the anchor bolts. Nuts or other fasteners are placed onto the portions of the anchor bolts protruding above the structural member and tightened. The sill plate is a member of a framed structure, which acts as the based upon which the frame is built. The sill plate is commonly a 2.times.4 or 2.times.6. Generally, the anchor bolts must protrude vertically or near-vertically to be of use in anchoring a structure, so that the sill plate can be placed onto them without interference and so that the nuts placed on the anchor bolts can exert a substantially downward force against the sill plate to hold it firmly against the slab.
Typically, the positioning of the anchor bolts relative to one another and relative to the edge of the concrete slab is important, and is generally set by the applicable building code. The position of the anchor bolts relative to one another is generally driven by the object or objects to be anchored. For example, if a frame wall is to be anchored to a concrete foundation, it typically contains several predrilled holes or apertures in its sill plate that correspond to the anchor bolts. Because the anchor bolts pass through those holes or apertures when that sill plate is placed onto them, the holes or apertures must match the relative positions of the anchor bolts. The position of the anchor bolts relative to the edge of the slab is driven by two primary factors. First, the anchor bolts cannot be too close to the edge of the foundation, or they may break through the resultant thin layer of concrete between them and the ground outside the foundation when subject to stress. Second, it is generally not desired for the anchor bolts to be too far from the edge of the foundation, or a portion of the foundation will be exposed after the structure is built on or placed on it.
Builders typically utilize some kind of apparatus to ensure that the anchor bolts are properly positioned in the concrete slab foundation. An apparatus in the prior art that has been used to position and hold anchor bolts while a concrete foundation is being poured is simply a wooden beam, such as a 2.times.4. Holes are drilled in the beam corresponding to the desired locations of the anchor bolts. A nut of larger diameter than the hole is screwed onto each anchor bolt, and each anchor bolt is then inserted into the beam so that it hangs through a hole, supported by contact between the nut and the upper surface of the beam. The beam is then placed across two mud walls such that the bottom portion of each anchor bolt protrudes into the space which the concrete will occupy after being poured. Using a beam to position and hold the anchor bolts has the advantages of accurately positioning the bolts relative to one another, and of securely holding the anchor bolts during foundation pouring.
The beam has several disadvantages. It is difficult to maintain a consistent distance from the edge of the mud wall to each bolt, because any misalignment of the beam affects all of the anchor bolts it holds. The beam requires significant labor to remove from the anchor bolts after the concrete has hardened. Each nut must be individually unscrewed from an anchor bolt, which can be difficult if wet concrete splashed onto and then dried on the threads. Further, use of the beam prevents masons from properly finishing out the surface of the concrete slab. As the concrete dries, masons typically finish it out with trowels and other tools in order to give it a smooth, flat surface. This is done to ensure that the structure sits flat on the slab. It also serves an aesthetic function, especially when the slab floor is not intended to be finished further, such as in a warehouse or industrial building. However, when the beam is used, masons can only trowel the slab up to the edge of the beam. If the concrete is poured slightly higher than the bottom of the beam, which is not uncommon, the beam will leave a rectangular depression in the finished slab that must be filled with additional concrete or with another material in order for the slab surface to be flat. Otherwise, a gap will exist between the slab and the wall or structure on top of it. Such a gap voids the thermal, moisture and pest barrier. Further, if the beam holding the anchor bolts is not parallel to the mud wall, the anchor bolts will not be parallel to the edge of the slab. As a result, walls of the structure that are attached to the anchor bolts may not meet at the intended angle. Finally, wet concrete can easily splash onto the threads of the anchor bolt during pouring. Typically, a portion of the threaded section of an anchor bolt sticks out above the beam, and is exposed to possible concrete splashes. After concrete splashes onto the threads and dries, it is difficult and time-consuming to remove. Removal of that dried concrete consumes valuable time, and can damage the threads of the anchor bolt.
Another apparatus that has been used to position and hold anchor bolts while a concrete foundation is being poured is a wire. Anchor bolts are secured to a wire, typically by wrapping the wire tightly around each anchor bolt. The anchor bolts are positioned relative to one another on the wire as they are desired to be positioned relative to one another when installed in the foundation. The wire is then strung between two supports such that the anchor bolts attached to it will be partly submerged into the concrete when poured. After the concrete has set, the wire must be unwrapped from the anchor bolt, and a mason trowels around and finishes out the concrete with the bolt in place. However, the wire provides minimal support for the anchor bolts. As the concrete is poured, the anchor bolts can easily deviate from a vertical position as the concrete moves and swirls, because the wire provides no lateral support. After the concrete dries, any anchor bolts which do not extend vertically have minimal utility at best; they may not fit through holes or apertures in the structure, and nuts or attachment devices screwed onto them will exert a noticeable lateral force as well as downward force, creating undesirable shear stress in the anchor bolts which can cause fatigue and eventual failure. The only solution is to break out the anchor bolt and re-pour that section of concrete. Re-poured sections are not as structurally sound, because the patched section does not substantially fuse with the hardened concrete around it. Unfortunately, some builders simply break out these bolts and do not replace them. Without the intended number of anchor bolts, the structure is not as securely attached to the foundation as it should be, and may not conform to the applicable building code.
Further, it is difficult to position the anchor bolts accurately when the anchor bolts are held by wrapping the wire around them. Precision winding is needed to ensure proper spacing between the bolts, precision which can be difficult to achieve at a busy work site. Further, as with the use of the wooden beam apparatus above, misalignment of the wire relative to the edge of the slab is possible, and has the same undesirable results. Finally, use of the wire provides almost no protection against wet concrete splashing on the threaded region of the anchor bolt, leading to the same undesirable consequences described with respect to the wooden beam apparatus.
Another device which has been used to position anchor bolts relative to a mud wall is a bolt holder. The bolt holder includes an open-ended guide tube for guiding an anchor bolt that protrudes vertically above a flat body. The flat body extends horizontally from the mud wall to which it is attached. An anchor bolt is inserted into the guide tube, and a nut or other fastener of greater diameter than the inner diameter of the guide tube is then attached to the threaded end of the anchor bolt. The nut thus rests on the top of the guide tube, suspending the anchor bolt therein. At the opposite end of the flat body member from the guide tube, a rear projection extends downward from the flat body member and abuts the rear surface of the mud wall.
Like the beam and the wire, the bolt holder possesses several disadvantages. As with the 2.times.4 apparatus, masons can only finish out the surface of the concrete slab up to the edge of the bolt holder. Further, the guide tube does not securely restrain an anchor bolt. The anchor bolt simply hangs by a nut from the hole in the end of the guide tube. If the concrete is poured slightly higher than the bottom of the bolt holder, which is not an uncommon occurrence, the apparatus will leave a rectangular depression in the finished slab that must be filled with additional concrete or with another material in order for the slab to be sufficiently flat. That depression is perpendicular to the sill plate, so if left unfilled, it will create a gap between the bottom member of a structure and the slab foundation which admits pests, moisture, and hot and cold air into the structure from outside. The bolt holder can adhere to the concrete slab if the slab is poured to a level above the lower surface of its body. In that situation, the apparatus generally must be removed from the dried slab with a degree of force that can damage or destroy it. Finally, the single projection possessed by the bolt holder limits it to accurate use with only one width of sill plate. If a sill plate of a different width is used, the anchor bolt may be placed too close to the edge of the slab or too far within it for proper use with that sill plate.